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Objective Reviews & Commentary - An Engineer's Perspective

November 2, 2011

C-Media CM119 DAC

INTRO: This is another in a series of inexpensive USB DACs such as the Turtle Beach Micro II I reviewed a few weeks ago and the Behringer UCA202. It’s the least expensive DAC I’ve tested with a street price around $13. This example is from Syba but there are similar products based on the same C-Media CM119 chip. So how does it measure up against the more expensive Micro II?

SYBA C-Media CM119: The CM119 is not only the cheapest USB DAC I know of but also the smallest. It's smaller than many flash thumb drives and has only microphone and headphone/line out jacks. The USB plug is part of the DAC. The housing is translucent and there’s a green LED inside that lights up when the CM119 is recognized by Windows. There’s no volume control or other controls. It doesn’t come with any accessories and should work fine on most PC’s without deeply recessed USB jacks. It may block access to nearby jacks as it’s considerably more bulky than a typical USB cable. If you have a jack problem, you can always get a USB extension cable or simply get a DAC that comes with such a “pigtail” like the Turtle Beach Micro II and others.

WINDOWS INSTALLATION: The CM119 installed smoothly in both XP and Windows 7 without needing any drivers. Windows reported it as a “Generic USB Audio Device”. The only sample rates and bit depths available are 16/44 and 16/48 as shown to the right in Windows 7 (click for larger).

SUBJECTIVE SOUND QUALITY: There was moderate hiss and noise with my Ultimate Ears IEMs and it was noticeably worse than the Turtle Beach Micro II. The sound quality with balanced armature Ultimate Ears and Mee M11+ 16 ohm dynamic IEMs was not very good. The bass performance was poor and the highs seemed noticeably harsh and “edgy”. Using the CM119 to drive my O2 amp was notably better but it still didn’t sound quite right.

MEASUREMENT SUMMARY: The overall results were not very impressive and in some ways worse than the already marginal Micro II. The CM119 struggles with headphones below 80 ohms resulting bass roll off and more distortion. The output impedance at 100 hz is marginally high while the high frequency distortion and jitter are relatively poor. Here are the results compared to the$25 Turtle Beach Micro II and the $30 Behringer UCA202. The scores are “A” (excellent) through “F” (unacceptable):

BOTTOM LINE: It was interesting to see how much USB DAC $13 will buy. It’s half the price of the Turtle Beach Micro II and has relatively similar performance. The CM119 at least doesn’t suffer from the Micro II’s dynamic range problem. But unless you have an especially lousy headphone output on your PC, the CM119 might be a step backwards. It could be useful as a second sound source allowing routing say your PC’s system sounds to inexpensive desktop speakers. It’s also OK for casual listening with inexpensive headphones or for skype/chat use. But for high quality listening, especially with headphones below 80 ohms, there are much better options for not much more money. Check back for more DAC reviews soon.

TECH SECTION

C-MEDIA CM119: The CM119 chip in this Syba DAC is similar to the CM102 in the Turtle Beach Micro II. Both integrate the USB interface, DAC, filtering, and headphone “amp” all on a single chip. While this keeps the size and price down, the performance isn’t that great. At least the CM119 doesn’t default to having dynamic range compression enabled like the CM102 in the Micro II. Many motherboard chipsets, like the better ones from Realtek, offer better overall performance.

LOADS USED: I used a 33 ohm load to represent typical portable headphones in the 16 – 80 ohm range and at 10K which is the typical input impedance of many headphone amps, such as the O2, and powered speakers. Performance into 22k or 50K loads will be very similar. I ran a few spot checks at 15 ohms, 80, 150, 600 and 100K ohms even if the results are not always shown in the graphs.

FREQUENCY RESPONSE: The frequency response with a 10K load (such as a headphone amp) at 16/44 is acceptable but not great. It’s down –1 dB at about 15 Khz. The steep roll off above 12 Khz is typical of a cheap DAC running at 44 Khz and is due to cost savings in the digital and analog filters and similar to the Micro II. This will likely create significant phase shift in upper audio range. The slight peak around 8 Khz is also disturbing and likely indicates poor DAC filtering. The biggest problem is what happens to the bass when you plug in headphones. The low frequency roll off is even worse than the Micro II. This is likely because the small size and/or tight budget didn’t leave much room for properly sized output capacitors. Into 16 ohms it’s 3 dB down at a very audible 100 hz. Into 33 ohms it’s –3 dB at 50 hz and – 6 dB at 20 hz which could still be audible with good headphones. Into 80 ohms it’s –3 dB at 20hz which is marginal but acceptable. With higher impedance headphones the bass response would be OK. The second graph shows the Micro II for comparison:

THD+N vs OUTPUT: The CM119, into 10K, is even worse than the Micro II. The distortion is fairly high at low levels and doesn’t fall below the desired 0.05% line until about 400 mV and hits a maximum output of 950 mV at 0 dBFS and full volume. Into 33 ohms the distortion is always above 0.05% and the max output is about 880 mV. This works out to 48 mW into 16 ohms, 24 mW into 32 ohms, 9 mW into 80 ohms, 5 mW into 300 ohms and 2.5 mW into 600 ohms. The second graph shows the Micro II for comparison (the trace colors are swapped):

100 hz 0 dBFS THD+N & OUTPUT IMPEDANCE: The undersized output capacitors hurt the CM119 at 100 hz in this test. Into 15 ohms it only managed 680 mV at full volume and 0 dBFS. But into 100K it managed 950 mV. That works out to a relatively poor output impedance of 5.9 ohms at 100 hz. At 1 Khz, where the output capacitors were much less of a problem, the output impedance is 1.1 ohms. The distortion was also relatively high—again partly due to the output capacitors. The second graph shows the Micro II for comparison which has significantly more output and a lower output impedance:

THD+N vs FREQUENCY: The CM119’s THD+Noise plotted from 20 hz to 20 Khz into 10K (yellow) was very similar to the Micro II and showed the same strange behavior above about 5 Khz. Into 33 ohms (blue) it was even worse than the Micro II hovering around or above 0.1%. This is relatively poor performance but might be acceptable for non-critical applications. The Micro II and Behringer UCA202 are shown at 10K in the second graph for comparison:

SMPTE IMD 33 OHMS: The result here is marginal. The third harmonic of nearly –70 dB at 180 hz is the biggest cause for alarm. The even bigger spike at 120 hz is more benign 2nd harmonic distortion which is less likely to be audible. The spikes above and near –80 dB around the 7 Khz signal are true IMD and also not a good sign. Overall, the CM119 scores a better reading on this test than the Micro II but that might be partly due to the slightly lower output level. This test was run at full volume at the highest digital output possible (just under 0 dBFS combined) but because of the undersize output capacitors, and lower overall output, the CM119 could only manage 613 mV. The second graph shows the Micro II for comparison at 0 dBu (775 mV) with a considerably bigger “IMD mountain” around the 7 Khz signal:

CCIF IMD MICRO II 44 Khz 33 Ohms: The CM119 wasn’t quite as awful as the Micro II on this test but it was still really bad with lots of distortion products above –80 dB. As with the SMPTE test above, I suspect the lower level helped out the CM119. The second graph shows the Micro II:

CCIF IMD MICRO II 44 Khz 10K: Into 10K the CM119 was nearly identical to the Micro II but neither is very respectable. The 48 Khz sampling rate was also similar to the Micro II. The second graph shows the Micro II for comparison while the third graph shows the vastly better performance of the $30 Behringer UCA202:

NOISE & LINEARITY: The weighted noise of the CM119 was about 5 dB worse than the Micro II and the un-weighted noise was about 3.5 dB higher. This is marginal noise performance but is still acceptable and similar to the UCA202. The linearity was very similar to the Micro II with less than 1 dB of error. The second graph shows the Micro II for comparison:

JITTER: Here’s the spectrum from the dScope’s J-Test for jitter. The result shows a lot of low frequency jitter (“spread” in the 11025 hz signal) but it’s slightly better than the Micro II. Still, it’s much worse than average even compared to the $30 UCA202. At least the frequency accuracy (clock accuracy) is very good as shown by the frequency reading on the left. The second graph shows the Micro II while the third graph shows the UCA202 for comparison. Note how the “spread” is confined to below –118 dB on the UCA202 but reaches up beyond –70 dB with the C-Media DACs:

TECH COMMENTS: The CM119 performs similarly to the marginal Turtle Beach Micro II but with even more severe low frequency roll off into headphones and even higher overall distortion. Used to drive an amp, powered speakers, or perhaps fairly sensitive dynamic headphone of 80 ohms or more it’s marginally acceptable for a low cost DAC. But it’s best used for non-critical applications like voice chat, Skype, etc. For high quality applications driving an amplifier or powered speakers the UCA202 offers much better overall performance. Check back for more DAC reviews soon.

@Satellite, good point. I should probably re-word that slightly. What I was trying to is they both have very similar problems and are much closer to each other than even something like the UCA202. The Syba is slightly worse in a few ways (LF roll off and overall distortion) and better in a few others (CCIF IMD and less jitter).

Hope to see the headphonia/headstage dac cable to be part of this test. It seems that it has been updated. On website still the old cable (headphonia.eu), review:http://www.headfonia.com/the-headstage-usb-dac-cable/

Also wondering which measurements influence preceived depth and width of "stage".

@Jlle, the Dac Cable isn't part of this test as it's considerably more expensive and it's only (AFAIK) available from one rather unreliable source. Their Arrow amp, for example, is no longer available and you have to wonder once Headphonia sells out of Dac Cables if they'll disappear too?

The Dac Cable is a similar design to the NuForce uDAC-2 and many other DACs using the TI DAC as only a USB interface providing I2S to a better DAC chip.

Soundstage spaciousness is much more a function of the headphones than the amp. But there is some correlation with phase error and the perceived soundstage. High levels of jitter may also degrade width and depth. Because of the poor digital/analog filtering, the C-Media based USB DACs I've tested likely have a lot of phase error and I've shown they have a lot of jitter. So it's reasonable to expect the C-Media DACs may sound worse.

A purely objective headphone review would be uber-cool, though I'm not sure how you could make that happen. Maybe a write-up on audiophile myths - like a #headfi Mythbuster special once in a while would be fun to read as well.

@s1009, sorry if you're bored but I appreciate the feedback. The idea with the cheap DACs was to try and find a highly portable inexpensive USB DAC to work with the O2 and other headphone amps. I have already published a general write up on audiophile myths. Check out: The Subjective vs Objective Debate

Most high-end products, to be honest, are a waste of money if you're buying them with the hope of getting better performance. Many perform much worse than much less expensive products. I have however tested some high end products such as my article on the Benchmark DAC1 Pre, review of the Sennheiser HD650, etc.

Hey NwAvGuy, thanks for (especially) all the great usb DAC reviews you've written, they're definitely the best and most usefull I've come across on the web so far.

I'm writing this somewhat offtopic comment because I'm currently looking for a relatively cheap usb DAC for use with my laptop. I'm considering the Fiio E7(+l7 line out), the behringer UCA202 (after reading your review of it) and a housed version of this PCM2706+WM8501 board: http://forum.lowyat.net/index.php?showtopic=1717494&hl=

For now I'll be using it primarily in combination with an entry level T-amp and a Sennheiser RS170 (wireless 'digital') headphone, though both may be upgraded in the future.

Anyway, several times you've mentioned on your blog that the way in which a chip has been implemented/used is often more important/of more influence then just what specific chip is being used. This being the case I was wondering what the thoughts of someone as knowledgeable as yourself are, when looking at the board I've linked to earlier in this comment. (..and if perhaps, you've had any experience with this board yourself, though I'm guessing there'd be a pretty small chance of that.)

Thanks again for all the time and effort you put into this blog, it's very informative and a true pleasure to read.

@Johnny, There are lots of eBay and similar DACs using the PCM27xxx for the USB interface and a better DAC chip like the WM8501. They're usually designed and sold by one person and the focus is on the components used rather than the proper design. The ones I've measured have all had problems--especially the ones with S/PDIF inputs.

Implementation really is critical and a lot of the people designing and selling boards like the one you linked lack the proper test equipment to even know if their designs work properly. If they did have such measurements, they could publish them. Some also, apparently, lack the proper knowledge to design audio gear correctly. I've seen some pretty bad mistakes.

DAC chips have many configuration options and some have very specific requirements for PC board layout, the I-V converter stage that follows the DAC, filtering, etc. And it's common for the "eBay" DACs to get one or more of those things wrong.

My best advice is to wait for my review on the FiiO E10 which should be a better, and cheaper, version of the E7. And unlike all those PCM27xxx based DACs it will do 24/96 over USB.

I love following your reviews on the budget audio components that many audio forums tend to ignore. Have you ever tested iPod Touch or iPhone for their DAC and/or amp performance? Would be interesting to have some reference point as whether its worth to seek upgrade over them or not.

@Anon, check the Sansa Clip+ review from February. I compare the Clip+ to my iPod Touch 3G. The only real issues with the Touch 3G are the approximately 7 ohm out impedance and not enough output for some headphones. Otherwise it performs surprisingly well. I think external DACs for iPods/iPhones are a waste of money.

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